How to know if a measurement tool is "good enough"

R

roder - 2012

#21
I understand that numbers 4:1 and 10:1 is not the same....
4:1, refers to accuracy of the instrument while 10:1 refers to the minimum resolution...

4:1 usually used to select a calibration standard at least 4x accurate to calibrate an instrument

10:1 usually used to select an instrument capable or has a minimum resolution/readability of 1/10 of the expected variation
 
Elsmar Forum Sponsor
T

True Position

#22
Sure, if a tool with 10:1 or 50:1 is “readily available”, and economical, efficient, and user-friendly, then by all means use it. But that is not always the case. I once had a 10:1 requirement from a major defense contractor for an electrical measurement. I had to go through quite a production to prove to them that at the current state-of-the-art such a measuring device was not commercially available anywhere at any price.

But don’t over-simplify and think that when using a 4:1 tool the risk of accepting a NC part is 25%. It is nowhere near there when a rigorous analysis is made. Hey – Juran ain’t no dummy, nor are the Boeing quality gurus.
The risk of accepting a NC part is not 25%, but for an area of 25% of the tolerance (both sides before the gage changes over to the next result) you can accept a NC part. (50% of the time either extreme result could be NC just due to basic prob) If you maintain a high cpk and don't use either extreme end of the tolerance you can be relatively sure that you are making good product.

Also, you are right in calling me out for blindly asking for 10 to 1, in many of the extreme cases (very small diameter tolerances, etc) finding something that can handle the resolution needed is not possible/cost effective. In the original posters issue though, micrometers are widely available.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#23
Also, you are right in calling me out for blindly asking for 10 to 1, in many of the extreme cases (very small diameter tolerances, etc) finding something that can handle the resolution needed is not possible/cost effective. In the original posters issue though, micrometers are widely available.
I am not so sure about giving the extreme cases a bye on this. Not being able to 'afford' a gage of adequate discrimination is not a very strong defense of rolling over an using an inadequate one. Either the callout was too conservative, and needs to be addressed (that issue of just because you can draw it does not mean you can make it or measure it), or you need to let someone that can provide the correct resources make the part. Otherwise, just use a pocket steel rule for everything - it will stand up to that standard. It is the favorite of those that use quality level TCE. :cool:
 
T

True Position

#24
I am not so sure about giving the extreme cases a bye on this. Not being able to 'afford' a gage of adequate discrimination is not a very strong defense of rolling over an using an inadequate one. Either the callout was too conservative, and needs to be addressed (that issue of just because you can draw it does not mean you can make it or measure it), or you need to let someone that can provide the correct resources make the part. Otherwise, just use a pocket steel rule for everything - it will stand up to that standard. It is the favorite of those that use quality level TCE. :cool:
Any time I break the 10 to 1 rule I clearly discuss it with my customer before hand. If they would like to bear the expense or purchasing/obtaining something better (or another company's services) that is their choice. I recently had some parts which had a total diameter tolerance of 0.006mm and while my supermic is supposedly accurate to 0.5 microns I still told them there was some risks associated with either extreme of the tolerance and I would let them know if any parts were at the extremes.

I just didn't want to be one of those people who always cry out 'You should have dealt with this during contract review!!'.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#25
Any time I break the 10 to 1 rule I clearly discuss it with my customer before hand. If they would like to bear the expense or purchasing/obtaining something better (or another company's services) that is their choice. I recently had some parts which had a total diameter tolerance of 0.006mm and while my supermic is supposedly accurate to 0.5 microns I still told them there was some risks associated with either extreme of the tolerance and I would let them know if any parts were at the extremes.
Good call. Just think, if they need that tolerance, most people are clueless on not only how to measure it, but also how to control it. How much of the tolerance is used up by roundness? How do you know? If you only measure one diameter and chuck it in the good bin, your customer will measure another one and reject the lot. It is a rule of life. After all, how many diameters are in a circle? Tighter tolerances need the discrimination more than the lesser, broad side of the barn ones, to have any idea what you are making. You will never detect the error of the process if your total error is mostly from measurement. 3:1 discrimination is for all practical purposes attribute.

I just didn't want to be one of those people who always cry out 'You should have dealt with this during contract review!!'.
Exactly! :agree1:
 
Thread starter Similar threads Forum Replies Date
O Dimension Measurement Tool Recommendation General Measurement Device and Calibration Topics 21
J Acme Thread Gage Tool Wear Measurement General Measurement Device and Calibration Topics 11
B What Measurement Tool to Choose for Plastic and Metal Parts Measurement Uncertainty (MU) 3
H Inspection Plan Preparation and Measurement Tool Requirements Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
J Using Pin Gages as a Measurement Tool for Ppk/Cpk studies Capability, Accuracy and Stability - Processes, Machines, etc. 11
C Automotive OEM Score Card Templates - Supplier performance measurement tool Supplier Quality Assurance and other Supplier Issues 18
D Gage R&R on a delta measurement - Particle measurement count tool Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
K 8.2.3.1 Monitoring and measurement of manufacturing processes - Tool change IATF 16949 - Automotive Quality Systems Standard 5
D ISO 9000 vs. SERVQUAL - System vs. Measurement Tool / Methodology ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
S How can Balanced scorecard (a measurement of performance tool) be used in ISO 9001? Quality Tools, Improvement and Analysis 6
M Measurement Uncertainty in Optical Microscopy Measurement Uncertainty (MU) 1
B ISO 6508 and portable hardness measurement instruments General Measurement Device and Calibration Topics 0
C How to Establish the Calibration & Measurement Capability (CMC)? ISO 17025 related Discussions 1
Ron Rompen Measurement of residual magnetism General Measurement Device and Calibration Topics 2
M Surgical angle measurement guide device with an application software Medical Device and FDA Regulations and Standards News 1
M Disabling measurement data during fault conditions IEC 60601 - Medical Electrical Equipment Safety Standards Series 5
J Most versatile measurement device General Measurement Device and Calibration Topics 2
P Surface scratch measurement General Measurement Device and Calibration Topics 1
N Drawing tolerance vs. Measurement device General Measurement Device and Calibration Topics 7
Ron Rompen MSA on automated measurement system - Multiple Step Vision System Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
P Thermo-Hygrometer - Measurement of 10DegC @10%RH ISO 17025 related Discussions 4
hogheavenfarm GDT Flatness measurement question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 10
K Software Validation for Measurement Tools used in Process Validation ISO 13485:2016 - Medical Device Quality Management Systems 2
K Best Measurement Systems Demos in California? General Measurement Device and Calibration Topics 1
M Measurement Error - How to determine what is acceptable? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
K Process Mapping - Inputs/Outputs/Detail Activities/Control points/Measurement? Process Maps, Process Mapping and Turtle Diagrams 4
B IEC 60601-2-10 - Accuracy of Pulse Parameters - Required Measurement Uncertainty IEC 60601 - Medical Electrical Equipment Safety Standards Series 3
N Program or application for standard time measurement in industry from video surveillance? Human Factors and Ergonomics in Engineering 1
M Defining frequency of measurement tools callibration Calibration and Metrology Software and Hardware 3
T How to “validate/qualify” a new measurement equipment? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
Bev D Verification and Validation of Measurement Systems Misc. Quality Assurance and Business Systems Related Topics 0
F How do you add accuracies for tools with different measurement devices? General Measurement Device and Calibration Topics 1
M Viable count Measurement ISO Standard Other Medical Device Related Standards 1
J Gauge R&R on a torque measurement Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 11
W Air Quality Measurement Hardware and Software General Measurement Device and Calibration Topics 11
G Does pitch/increment/resolution of a ruled scale apply to measurement uncertainty as line item? Measurement Uncertainty (MU) 10
Marco Bernardi Plane measurement with a 3D touch machine like a CMM. Calibration and Metrology Software and Hardware 3
Marco Bernardi Diameters measurement with 3D touch machine like a CMM Calibration and Metrology Software and Hardware 4
R Uncertainty in measurement larger than tolerance Measurement Uncertainty (MU) 2
R Measurement Uncertainties Budget for Thermometer Measurement Uncertainty (MU) 6
O Performance Measurement ISO 9001: 2015 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
O Monitoring performance - How do I determine performance measurement basis within my organization? Misc. Quality Assurance and Business Systems Related Topics 4
G What information to put on measurement Dimensional Results APQP and PPAP 7
D O Ring capability and measurement - What is the automotive 'norm' for capability studies on O Rings? General Measurement Device and Calibration Topics 3
F Electrical Metrology (Source/Generation and Measurement) General Measurement Device and Calibration Topics 1
G Gauge R&R on multiple dimensions using 3D measurement system Capability, Accuracy and Stability - Processes, Machines, etc. 6
F Measurement Audit and ILC for ISO 17025 Clause 7.7.2 - Comparison with results of other laboratories ISO 17025 related Discussions 0
Emran.mi Measurement system analysis - Can you help me about implementation MSA for CMM device Manufacturing and Related Processes 2
K ISO 17025:2017 clause 7.6.2 - Performing calibration of its own equipment shall evaluate the measurement uncertainty ISO 17025 related Discussions 6
Q How should I analyze measurement correlation between me and customer? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12

Similar threads

Top Bottom